The present invention relates to a method of forming a multilayered film of a titanium (Ti) film or the like between an electrode and wiring of a semiconductor circuit device.
Recently, to satisfy the requirements for high density and high integration of circuit elements in manufacturing the semiconductor device, a multilayered wiring structure tends to be employed as the semiconductor circuit. In this circumstance, a technique for electrically connecting a circuit element formed in a silicon substrate to an upper wiring layer through a contact hole and mutually connecting an upper wiring layer and a lower wiring layer through a via hole becomes important. To be more specific, a technique for burying a metal in the contact hole and the via-hole becomes important.
As the metal to be buried in the contact hole and the via-hole, aluminium (Al) or tungsten (W), or an alloy mainly made of the aforementioned metal, is generally employed. However, in the case where the metal or the alloy is in direct contact with the silicon substrate or an Al wiring, if annealing is applied in a later step, an alloy of the buried metal and Si or Al is likely to be formed in the boundary portion between them since Al absorbs the contact metal. The formation of such an alloy is not preferable since the alloy has a large electric resistance. The alloy, due to the large electric resistance, works against a reduction of power consumption and a speedy operation recently required for the device.
It is also not preferable to use W or a W alloy as the buried layer of the contact hole, since WF.sub.6 gas, for use in burying W or the W alloy, penetrates into the Si substrate and degrading electric characteristics of the device.
To prevent the aforementioned undesirable features, a contact metal layer is formed as a barrier layer on the Si substrate and the inner wall of the contact hole or the via-hole so that the contact metal layer may be interposed between the buried metal layer and the Si substrate or the inner wall.
As the contact metal layer, a two-layered film constituting of a Ti film and a TiN film, is generally employed. The two-layered contact metal layer is conventionally formed by a physical vapor deposition (PVD) method. However, with the tendency for fine patterns and high integration of the circuit device, wiring width and an aperture of the holes has been reduced.
In addition to this, the holes tend to be formed in a higher aspect ratio, recently. For these reasons, a chemical vapor deposition (CVD) method has been increasingly employed since the CVD method is also suitable for forming the holes of the higher aspect ratio.
However, in this case where TiCl.sub.4 is employed as the reaction gas in the CVD method, Cl.sub.2 and HCl generate as by-products. Since these gases etch the Ti film, the TiN film loses sufficient contact with the Ti film. As a result, TiN film removes from the Ti film, increasing contact resistance.
To overcome the increase in contact resistance, a method in which the TiN film is formed after the Ti film surface is nitrided with nitrogen gas and hydrogen gas, is proposed by the present inventors (filed as U.S. Pat. No. 941,272).
According to this method, since the Ti film surface is protected with a thin nitride film, the Ti film is prevented from being etched, reducing the contact resistance.
However, the thin nitride film thus formed on the Ti film surface does not always exhibit a sufficient effect for preventing etching of the Ti film surface. As a matter of fact, it is known that the TiN film sometimes removes from the Ti film, thereby increasing the contact resistance.
The occurrence of film removal is not limited to the case where the TiN film is formed on the Ti film and may arise in the case where another type of film is formed on the Ti film by using a halogen containing gas. Hence, it has been desired to find effective means to overcome the film removal.